The harmonious development among economy, energy and environment is necessary for the modernization of a country. In order to solve the problems of continuous depletion of fossil-fuel energy (oil, coal, etc.) which is non-renewable and does environmental influences, the development of renewable energy sources has been regarded as a specific goal for the future plans in our country and some other developed ones. Wind energy is one of the important, clean, renewable energy sources which would not influence the environment, while the wind power generation is the most quickly developed, technical form which involves scale development and utilization at present. Now the wind power energy has constituted a scale industrial chain.
A wind-driven energy generator basically comprises three units: a primary energy conversion unit, a mechanical energy transfer unit and a generation unit. Wind power is the primary energy of the wind-driven power generation. The primary energy conversion unit mainly functions for the conversion from wind power into rotational mechanical energy (torque). Then the mechanical energy transfer unit and the electric power generation unit connected thereto are driven by means of wind wheels and wind wheel shafts, to constitute an integral, wind-driven power generating device. Thus, the primary energy conversion unit becomes the core part of the wind-driven power generating device.
The primary energy conversion unit comprises wind wheels, power controllers (speed regulators) and other components, wherein the wind wheel is consisted of blades and wheel hubs with good aerodynamic shapes. Currently, the wind-driven power generator set with horizontal shaft usually uses three blades wind wheel. After hundreds of years of research and improvement, such wind wheel can provide certain efficiency, which allows the set operating smoothly, and allows substantially eliminating systematic and cyclic loads, so as to output stable torque. However, it results in that the wind power utilization ratio is actually lower than Betz limit. It is believed by many authorities and units that the wind power utilization ratio provided by such wind wheels is only about 25%. Additionally, in order to maintain the rotational speed at a rated value of the generator, such wind wheel must adopt a speed regulation device having variable propeller pitch or adopt a blade stall control device having fixed propeller pitch with complicated structures, either of which leads to a very high production cost. Another big problem is that the diameter of the wind wheel has to be larger to increase the power for a single set. The diameter for an impeller of a 6 MW wind turbine will exceed 120 meters. Such a large diameter causes great difficulties to the production, transportation, installation and maintenance of blades, and considerably increases the production cost for equipments. Since the diameter of the wind wheel increases, the height of tower rack will be greatly raised, which also causes the same difficulties, and also greatly increases the production cost. Additionally, current wind-driven power generator set with vertical shaft involves more defects. This type of wind-driven power generator set is featured in that the wind wheel rotates around a vertical axis, so as to receive in-coming wind from all directions, without the need to dispose a deviation device towards the wind having complicated structure. Transmission chains and the generator can be installed on the ground so that it is convenient for maintenance. Thus the production cost for the equipments with such structure will be low. However, the most noticeable defect for current wind-driven power generator set with vertical shaft is the low wind power utilization ratio. In order to shorten the transmission shaft, such power generator set is usually installed relatively closer to the ground, thus the available wind power resource is limited, which makes the activation of wind wheels being difficult. With respect to the currently utilized forms of vertical shaft type and horizontal shaft type wind-driven power generator sets, the differences in aerodynamics and structures are relatively large, and the vertical shaft type is far less than the horizontal shaft type in terms of underlying research and technology maturity. Due to the reasons above, although the vertical shaft has many advantages thereof, its development has been limited.